Rob Edwards is a freelance environmental journalist with the Sunday Herald and New Scientist.

The news release was pretty clear. "Chernobyl: The True Scale of the Accident" was the headline. "UN report provides definitive answers" said the subheading. And then, the opening paragraph:

"A total of up to four thousand people could eventually die of radiation exposure from the Chernobyl nuclear power plant accident nearly 20 years ago, an international team of more than 100 scientists has concluded."

Only one problem: it wasn't true.

Chernobyl reactor number four in Ukraine was ripped apart by an explosion on 26 April 1986. It burned for ten days and spewed a massive amount of radioactivity over Europe and the rest of the world  100 times more than that from the atom bombs that devastated Hiroshima and Nagasaki in 1945.

In September 2005, a clutch of United Nations organisations led by the International Atomic Energy Agency (IAEA) and the World Health Organisation (WHO), issued their "definitive" news release about it. As it was meant to, it led to headlines around the world suggesting that the accident would only kill 4,000  a message which the WHO said at the time was "reassuring".

But in the run-up to Chernobyl's twentieth anniversary over the last few weeks, the UN report has been thoroughly discredited. A report by two independent radiation scientists, Ian Fairlie and David Sumner, said the global death toll from cancers was actually going to be between 30,000 and 60,000.

They pointed out that the UN report had only counted cancer deaths from the most contaminated parts of the three nearest countries: Ukraine, Belarus and Russia. It had omitted deaths in the less contaminated areas of these countries, and from the rest of Europe and the world. This was odd, to say the least, especially as the majority of the radioactivity actually fell beyond the borders of those three countries.

A series of other studies since have come up with similarly high, or higher, numbers. The WHO's International Agency for Research on Cancer in Lyon, France, published a study which put the cancer death toll in Europe at "about 16,000". Allowing for the uncertainties of estimating deaths caused by exposure to low-level radiation, the figure could range from 6,700 to 38,000, it said.

One of the study's authors, Elizabeth Cardis, pointed out the Chernobyl cancers will only be a very small fraction of those due to other causes and so will be very difficult to detect. But this doesn't mean that they should be ignored, she said. "These figures all reflect human suffering and death."

The environmental group, Greenpeace, released a report quoting Russian scientists who suggested that radiation from Chernobyl could kill as many as 90,000. And the European Committee of Radiation Risk published a book by Chris Busby & Alexey Yablokov claiming "millions" of cancer deaths.

Critically, the WHO itself issued a new statement. It said: "WHO estimates there may be up to 9,000 excess cancer deaths due to Chernobyl among the people who worked on the clean-up operations, evacuees and residents of the highly and lower-contaminated regions in Belarus, the Russian Federation and Ukraine."

Also on openDemocracy about the twentieth anniversary of the Chernobyl nuclear disaster:

"Nuclear energy by fission is not as clean, safe, or economical as the powerful lobbies for it would have us believe"

In an associated factsheet, the WHO also accepted that the radiation released would cause cancers in other parts of Europe. But it declined to estimate numbers, saying merely that predictions are "very uncertain".

Zhanat Carr, a radiation scientist with the WHO in Geneva, admitted to New Scientist that the September news release, and the report that backed it up, had been a "political communication tool". She stated: "Scientifically, it may not be the best approach."

The WHO, in other words, has effectively disowned 4,000 deaths as a headline figure. Even the IAEA, whose mission has always been to promote nuclear power, has wobbled a little. Put on the spot, the IAEA argued that the total of 4,000 deaths was highlighted to counter much higher figures claimed earlier by some.

"It was a bold action to put out a new figure that was much less than conventional wisdom", an IAEA spokeswoman reported.

"Bold" is one way of putting it. "Economical with the truth" would be another. Who knows exactly what international politicking went on behind the scenes between the IAEA and the WHO over the wording of the misleading news release? But it looks like the IAEA, a much more powerful organisation than the WHO within the United Nations system, called the shots.

The IAEA spin doctors must have been proud of their work when the stories spread across the world's media stressing how few deaths Chernobyl had caused. But now it has all been undone.

We will probably never know for sure how many people will be killed by the world's worst nuclear accident, but we can be sure of one thing. It's going to be a hell of a lot more than 4,000.